As either a part of the manufacturing process or after completion of the manufacturing process, motor-vehicle control units, which include micro-controllers, for example, must be tested for their functionality at the factory. To this end, special software functions, which are only used to test the control units at the factory and are no longer necessary during later operation by the actual user, must be provided in the control unit. Such special functions (or test functions) may not be executable during the future operation of the control units, since unwanted behavior of the control unit could otherwise be produced. In a motor vehicle, this would produce, for example, an unacceptable safety risk during normal operation, e.g., when control units of safety-relevant components such as the drive system or the brake system would execute manufacturer test functions.
Because of this, a special test or factory mode is generally defined, which is only implemented after a so-called entry condition is satisfied. In the case of engine control units, it is known that such an entry condition may be generated by applying predefined signals at input pins or terminals for the connection of sensors. In this context, the signals applied are signals which may not occur during normal operation of the engine. In this manner, it is ensured that an inadvertent jump into the test mode may not occur during normal operation.
In the above-explained design approach, it is disadvantageous that, in addition to the communication lines such as CAN lines or K lines, additional connector pins such as sensor connections are necessary for applying the signals for providing the entry condition. However, control units, which only have a supply-voltage connection and data-bus connection, do not provide any additional control-unit pins, via which signals may be applied to provide an entry condition to the control unit to be tested at the factory.